The present invention relates to nuclear reactors, particularly of the pressurized water type, incorporating a pressure enclosure containing the reactor core, called the vessel and at least one steam generator cooling the primary liquid by evaporating the secondary liquid.
The steam generators used in pressurized water reactors can be of the "single pass type". In this type of generator, the primary fluid generally enters via the upper end of the generator and leaves by the lower end. Single pass generators are to be compared with U-tube steam generators in which the primary fluid enters and leaves by the lower end of the generator. In U-tube generators, the secondary fluid mass is relatively large, whilst it is very small in the case of single pass generators and in actual fact 100 times lower in the case of compact, plate-type steam generators.
If it is necessary to stop the supply pump for the secondary circuit or suddenly close the valve supplying the secondary generator with secondary fluid in the liquid state, the removal of the residual power of the reactor takes place by reacting the secondary fluid in the steam generators before the stand-by circuits or systems come into action. The mass of secondary fluid contained in U-tube steam generators is generally sufficient to enable a removal of the residual power during a sufficiently long period of time before starting up the stand-by circuit, but this is not the case with regard to the secondary fluid mass contained in single pass steam generators. The value given hereinbefore shows that a plate-type steam generator has virtually a zero inertia.
When the steam generators used in pressurized water reactors are of the single pass type, it is therefore of interest or even necessary to increase the inertia of the generators so that the stand-by circuits come into action under favourable conditions.